The invention is directed to a method for transporting commodities, especially liquid commodities above their congealing temperature in tanks or tank containers, wherein at least a partial flow of the hot exhaust gases of the internal combustion engine of a tank- or tank container-vehicle flows through a heat exchanger, through which heat transfer oil passes in a closed cycle and which yields heat to the heat transfer oil and/or wherein an electrically heated heat exchanger yields heat to the heat transfer oil and the heat transfer oil transfers heat to the commodity through the tank or tank container wall designed as a heat exchanger, as well as an apparatus for performing the method.
Furthermore, the invention is directed to a method for cleaning tanks and tank containers after the transport of the commodities has been terminated, especially after termination of transporting liquid commodities above their congealing temperature, with a cleaning agent, which can be a cleaning solution, water (cold and/or hot water) and/or steam.
In the sense of the invention the commodities to be transported include liquid, pasty, pourable or fluid, generally speaking heapable bulk goods, among these oils, resins, varnishes, granulates, furthermore foodstuffs, such as olive oil, liquefied eggs, milk and the like. The invention means by liquid, especially such commodities to be transported above their congealing temperature, commodities whose congealing temperature is such, that under the prevailing environmental temperatures they can at least partially congeal in the tanks or tank containers, wherein mainly those tanks and tank containers in the region of the rear axle of the tractor trailer units can be exposed to an increased or accelerated cooling due to the high velocities of the head wind.
Examples of these commodities are phthalate anhydride, maleic anhydride, greases, tar products etc., which are transported from chemical plants to the processing plants which fabricate end products therefrom.
These difficulties in transportation result from the circumstance that the congealing temperatures generally lie far above the usual air temperatures, meaning the environmental temperatures, for instance they are 130.degree. C. for phthalate anhydride, whose loading or charging temperature amounts to 160.degree. C.
Thus there always exists the danger that these products congeal at least partially or arrive at the processing plants in a congealed state. In these cases they must be brought to a sufficiently high temperature prior to draining from the tank.
In actual practice one passed for a long time past steam from stationary steam generation plants at a pressure of approximately 5 to 7 bar through tubes or semi-round tubes welded to the tanks.
Up to recently it was only possible to perform long distance transport of these products also in conditions for extreme cold in this manner.
Apart from these problems additional disadvantages arise: If a product which is only partially congealed is heated, local overheating occurs and with this also discolorations so that the product is no longer usable.
The reason for this lies above all in the circumstance that, even after only a partial congealing, a product can no longer circulate in all regions to the required extent when heated, so that a local overheating can be avoided.
At the same time a temperature reduction of the charged product through heat losses to the cold tank occurred since generally en route no or insufficient addition of heat could be assured. Tests with electrical heating belts have also become known which belts were wound around a tank wall cf tank trailer cars.
It was however seen that this type of heat transfer to the product required considerable amounts of energy and that the heat transfer from the heating belts to the tank was bad.
A marked source of danger consists in accumulation of vapors of the chemical products in the insulation, which can trigger explosions in case of faulty electrical installations.
Tractor trailer units for transportation of liquid commodities are known for solving these problems (De-OS 34 11 358.4-16).
They comprise a heat exchanger flanged directly downstream of the exhaust manifold, through whose bundle of tubes flows at least a partial stream of the hot exhaust gases of the internal combustion engine and past which flows heat transfer oil.
The heat transfer oil is contained in a closed cycle circulation and yields the heat it has absorbed to the contents of the tank.
It was seen that the transportation of liquid commodities above their congealing temperature is securely assured also at extremely low temperature and/or during long distance travel and that stops at substations for the purpose of heating the contents of the tank are no longer required en route.
Because of the high heat capacity of the heat transfer oil already relatively small quantities are sufficient, in order to assure reliably in tractor trailer trucks, that even a partial congealing of the contents of the tank is eliminated by appropriate flow velocities of the heat transfer oil.
The same applies to tank containers.
When delivering to a chemical plant or in the course of pickups at a chemical plant or a loading point the tank can be preheated to the temperature of the liquid commodity to be charged or loaded, so that stresses of the tank material are considerably reduced even at extremely low outside temperatures.
At the same time the temperature drop of the product in the tank is considerably reduced and in the course of the travel heat is continuously supplied to the tank by the heat transfer oil, so that the temperature fluctuations caused by this hitherto in the tank wall are eliminated and no cold spots at which the contents of the tank could congeal can arise in the tank, especially in the region of the domes and the valves.
The same problems arise if liquid commodities whose congealing temperatures lie above the environmental temperatures must be transported in tank containers.
Tank containers comprise frames consisting of box sections, whose dimensions correspond to the dimensions of the containers and where tanks for transportation of liquid commodities are arranged.
These tank containers are transported on the highway like conventional containers, they are reloaded in ports and container stations onto ships or open freight cars. They are reloaded again at a destination point and transported on the highway to their ultimate destination.
It is known to provide tank containers also with electrical heating belts or tapes (prospectus of the firm Holvrieka, B. V. in the Rotterdam area), in order to transmit heat to the tank container during transportation on the highway.
For this purpose the tractor trailer trucks include an electric generator coupled with an internal combustion engine and arranged as a structural unit behind the operator cab of the tractor trailer truck. Electrical couplings produce the detachable connection with the heating belts or tapes.
These tank containers are connected to the ship's electrical network, after they have been reloaded onto ships. It was however seen in actual practice, that already during highway transport a cooling and at least a partial congealing of the contents of the tank container could not be altogether avoided by the electrical heating of the tank. The additional heat losses of the tank contents during the reloading must be added hereto, which results in a further cooling.
Furthermore it was seen in actual practice that it is impossible to reheat a product, which has cooled in the time interval required for reloading the containers onto ships, to the original temperature by means of the heating tapes arranged on the tank wall.
Presumably no sufficient motion in the tank content (stirring effect) for a temperature compensation occurs any longer below a respective specific temperature for the previously defined liquid commodities, so that then local overheating occurs, which can entail product discoloration.
Similar problems arise with tank containers during rail or waterborne transport, if said containers are reloaded from the highway onto rail cars or onto a ship or in reverse. Furthermore heatable tank containers for the combined transport of liquid commodities on the highway on the rail or on water above their congealing temperatures in the heatable tank containers are known (DE-OS 36 23 145), which assure that the liquid commodities are maintained above their congealing temperatures also at extremely low ambient temperatures and/or long distances traveled and/or long reloading times and/or long periods while parked and/or long transportation interruptions.
For this purpose heat transfer oil circulating in a closed cycle absorbs heat from a heat exchanger during transport of a tank container on the highway, through which heat exchanger combustion gases of a road vehicle hauling the tank container flow. The heat transfer oil circulating in a closed cycle extracts heat from an electrically heated heat exchanger during rail-borne or water-borne transport of the tank container and transfers the heat thus removed through the tank wall designed as a heat exchanger to the contents of the tank.
Basically the supply of calrods with electrical energy in the course of water or rail-borne transport can be accomplished by a generator which is coupled with the internal combustion engine.
During transport of the tank container by rail electrical energy is fed into the electrically heatable heat exchanger by the overhead line of the railroad electrical supply network and during water-borne transport it is fed into the electrically heated heat exchanger from the shipboard electrical network of the transportation vessel.
The energy supply from the overhead line of the railroad network is accomplished simply by having electrical supply lines extend from the electric locomotive to the transport cars of the tank containers.
Many products must not only be transported above their congealing temperature, rather it is required in many cases that the maximum upper temperature is not exceeded, this for instance in the case of greases and oils.
Furthermore chemical products exist which become unstable and disintegrate below a lower limit temperature and which decompose above an upper limit temperature.
Thus the chemical product of the firm ICC marketed under the trademark Peg 4000 has a lower limit temperature of 115.degree. C. and an upper limit temperature of 125.degree. C. and is to be transported at an average temperature of about 120.degree. C.
A complication which such commodities is that, because of the high market price, they are often transported in small quantities of several hundred liters, while conventional tanks and tank containers have a volumetric capacity of 30,000 liters or above.
It must be added that the shipping is to be performed whatever the environmental temperatures, meaning sometimes at -30.degree. C. and sometimes at above 40.degree. C.
It also must be said that the exhaust gas quantities of the internal combustion engines fluctuate greatly in view of the frequent load changes and that the exhaust gas temperatures are also subject to great fluctuations.